Piston valves



Dec. 24, 1963 D. FIRTH ETAL 3,115,066

PISTON VALVES Filed April 29. 1960 Patented Dec. 2' 5, 1963 3,115,066PESTGN VALVES Donald Firth and James Duncan Hamilton, East Kilhrx ie,

Glasgow, Scotland, assignors to Council For Scientific and industrialResearch, London, England, a body corporate of the United Kingdom FiledApr. 29, 1960, Ser. No. 25,743 Claims priority, application GreatBritain May 4, 1959 4 Claims. (Cl. 1-250) This invention relates topiston valves and particularly, but not exclusively, piston valves forfluid pressure pumps or motors of the reciprocatory type and has for anobject to improve the operation thereof.

In hydraulic pumps and motors especially of the kind in which the pistonis always displaced on its outward stroke by fluid pressure and onlypositively displaced on its inward stroke, there is a risk of hammeringor shock wave conditions being set up in the cylinder when the valvemechanism changes over to admit either the low pressure chargingfluid-in the case of pumps-or the high pressure working fluid-in thecase of motorsto the working cylinder. For example, in aneccentric-andslipper type of pump, the working cylinder contains a smallvolume of fluid at the high delivery pressure at the instant of cut-oil.of the outlet valve. It is then exposed to the relatively low pressureinlet circuit at the instant of opening of the inlet valve. This cancause hammering and shock waves in the inlet circuit and producesroughness in the pump particularly at high speeds. In the case of amotor which operates on the same principle, the same effect obtains atthe instant when the piston has exhausted through the outlet valve andthe inlet valve opens to admit high pressure fluid.

In order to avoid the recurrent shocks mentioned above, the presentinvention provides variable timing of one or both of the valves so as toensure that the pressure conditions within the cylinder at the instantof changeover from one stroke to the next approximate to the newpressure conditions which will prevail at the commencement of the nextstroke.

This is achieved, according to the present invention, by means of apiston valve which works in a ported sleeve, the port being permanentlyin communication with a port in the cylinder. The sleeve is adjustablerelative to the piston so as to vary the instant of opening or ofcut-off, according to the function of the valve (i.e., whether it is aninlet or exhaust valve). This may be effected manually or automatically,according to preference, and the sleeve may have more than one portwhose events are controlled by the piston. To eficct said adjustment,the port or ports and the valve piston have helical operative edges andthe sleeve and valve piston are angularly adjustable relative to oneanother.

In the case of an hydraulic motor where the piston drives an eccentricthrough a slipper, the timing of the outlet valve is convenientlyadjusted to cause the valve to close a few degrees before T.D.C. so thatthe residual oil left in the cylinder from the exhaust stroke iscompressed to approximately the inlet pressure. In the case of a pump,on the other hand, the timing of the inlet valve is preferably delayedby a few degrees after T.D.C. to allow the residual oil trapped in thecylinder after a delivery stroke to expand until its pressureapproximates to the inlet pressure.

By the above arrangement a smooth transition can be achieved between onestroke and the next in the vicinity of T.D.C. with a consequentimprovement in the smoothness of operation of the pump or motor.

In order to ensure that this smooth transition is effected under allconditions of operation, the valve timing is preferably arranged to be afunction of the speed or load on the pump or motor.

A practical embodiment of the invention, as applied to a multi-cylinderhydraulic motor, will noW be particularly described with reference tothe accompanying drawing which is a section through a cylinder andassociated valve gear of a radial hydraulic motor or pump, the sectionbeing taken on a radial plane including the axis of the shaft.

In the drawing, the driven member of the motor is an eccentric l1 whichis engaged by the slipper 2 of each piston rod 3. The little end 4 ofthe rod is part spherical and is held in a seating 5 within the piston6. The piston works in a cylinder 7 in the main cylinder block 8 of themotor and is closed by a head 9. The piston 6 is shown in the drawingsin the T.D.C. position and the clearance volume ill is open either topressure or to exhaust through an inlet port 1111 or an outlet port 112respectively. The inlet port 11 is controlled by an inlet valve 13 andthe outlet port 112 is controlled by an outlet valve 14-.

Both valves 13, 14 are of generally identical construction and areoperated by tappets 15 from respective inlet and exhaust cams 1 6, '17.Each tappet slides in a bush 21 pressed into a socket in the cylinderblock 8.

The piston valves '13 and 14 are each of generally tubular form havingspaced upper and lower external lands 23, 24. The reduced diameter sternportion 25 between the lands registers with an inlet 66 or an outlet 61described in detail later. The lands -23, 24 form pressure fluid sealswithin a respective valve bore 28 or 29, the upper land 23 serving alsoto open and close the inlet or exhaust port 11, 12. The length of thestem 25 between lands is such as to ensure that the inlet or outlet 61is never cut off during the valve stroke. Within each valve bore is asleeve or liner 50 within which the piston 14 itself actuallyreciprocates.

In the upper end of each sleeve 50 is a series of ports 152, eachsymmetrically disposed, around the sleeve periphery, about an imaginaryhelical line 57. Each port 152, when developed on a plane tangential tothe sleeve St has the shape of a parallelogram.

Each port 152 is permanently in register with an annular inlet portgroove 53 (connected to the inlet port 11) or outlet port groove 59(connected to the outlet port 12) in the respective valve bore 28 or 29in the main block 8. Below the inlet port groove 53 a pressure fluidinlet groove 69 is machined around the internal wall of the inlet valvebore 2%, whilst a similar exhaust groove 61 is machined around theinternal wall of the outlet valve bore 29. Radial ports 62 in eachsleeve 5t? register with the respective grooves 6t 61.

The upper land 23 of each valve 13 or 14 has its operative or workingedge 63 of helical form, the pitch of the helix being the same as thatof the helical axis of symmetry 57 of each of the ports 152. (In thedrawing, the upper land 23 of the valve 13 is shown in its upperposition for convenience of illustrating the ports 152.) Each lower land24 of each valve has a radial working edge opposed to the helical edge63 of the upper land and the reduced stem section 25 in which is formedwith a longitudinal slot 64. This slot is engaged by a peg or spigot 65screwed into the block 8 and projecting through one of the sleeve ports62 to prevent rotation of the valve about its axis.

Since the lower or working edge 63 of the upper land 23 of each valvehas the same contour as the axis of symmetry 57 of the ports 152, theupper land controls the ports 152 in the same way as it would if it wereradial and the ports were symmetrical about a circumference of thesleeve Sit, in the conventional manner of piston valves. However, for afixed stroke of the valve 13 or 14 and a constant relation between theinlet or exhaust cam 16, 17 respectively and the piston 6, the valvetiming will depend on the relative angular orientations of the land 23and the sleeve 5t). Thus, by rotation of the latter within the valvebore 23 or 29 whilst the valve 13 or 1 is angularly locked by engagementof the peg 65 in the siot 6 opening or cut-ofi of the inlet or outletports 11 or 12 of the main cylinder 10 can be varied to occur atdifferent points in the stroke of the valve 13 or 14.

For xarnple, let it be assumed that the valve 13 is in the positionwhere the helical working edge 63 of its upper land 23 coincides withthe position shown in the drawing of the axis of symmetry 57 of theports 152. In this position, the ports are half closed by the land 23.If, now, the valve 13 remains stationary and the sleeve 50 is rotatedclockwise, as seen from above, the upper Wall 1520 of each port willapproach a position of coincidence with the working edge 63 of the land2T=i.e. the ports will progressively open.

On the other hand, if the sleeve 50 is rotated counterclockwise, thelower wall 152]) of each port will approach a position of coincidencewith the working edge 63 and the ports 152 will progressively close.

The instants of etfective closing and opening of the ports 11 and 12 canthus be adjusted to suit the working conditions of the motor, eithermanually or automatically. An automatic control would respond to thespeed or load on the motor, or both, and can be of any preferredconstruction.

In order to allow for a suitable area of aperture of the ports 152 and ahelix pitch which is sufiiciently coarse to give the necessary range oftiming control without excessive angular adjustment of the sleeve 50, itis preferred to form each port 152 with the central axis of how of fluidtherethrough inclined, in a plane containing the valve axis, to a radiusof the sleeve 50 in that plane. The angle of this incliniation will bedetermined, in any particular case, by the angular spread of the ports152, their height in the axial direction, and the desired or permissibleheight in the same direction of the annular groove 58, the latterconsideration being dictated by the requirement that the aperture ofeach port 152 in the outer wall of the sleeve 50 must fully registerwith the groove. In the arrangement illustrated in FIG. 1, thegeneratrices of the upper and lower walls 152a, 1521) of each port havea constant inclination to the valve axis, so that the angle ofinclination of the flow axis of the port is equal to the angle 5.

In order to facilitate the smooth action of the rotatable sleeve 50during timing adjustment, it must be a sliding fit within the valve bore23 or 29, and this may lead to the leakage of high pressure workingfluid into the resultant clearance space which may, in turn, cause anundesirable build-up of pressure. To prevent this, radial drain grooves70 are machined across each end of the sleeve 50. Each sleeve 5! isrotatable under the control of a cylindrical rack 55 engageable withpinion teeth 54- formed around part of the periphery of the sleeve 50.The rack is housed in a bore 56 in the cylinder block 3.

A spring 35 is housed in an axial counterbore 66 in the upper land 23 ofthe valve 13 or 14 and bears at its upper end against a shallow recessedscrew cap 67 threaded into the top end of the valve bore 23 or 29. Aninternal shoulder 68 in the counterbore constitutes the lower abutmentfor the spring 35, and the counterbore is continued at 69 with reduceddiameter to open through the lower end face of the valve 13 or 14 toprovide a drainage and pressure relief passage for fluid which 4 mayotherwise become trapped above the upper land 23.

We claim:

1. In a hydraulic positive displacement machine, a piston valvecomprising a sleeve; a port in said sleeve adapted to communicate with aworking cylinder of the machine and having a helical operative edge; avalve member reciprocable in said sleeve; a land on said valve memberhaving a control edge of helical form to register with the helicaloperative edge of said port and having an angular extent greater thanthat of said operative edge of said port; and means for adjusting theangular displacement of said sleeve about its longitudinal axis.

2. In a hydraulic positive displacement machine, a piston valveaccording to claim 1 wherein said valve member is engageable with acoacting fixed formation for preventing rotation of said member aboutits axis.

3. In a fluid pressure machine, a closed work cylin der including atleast one lateral port through which fluid will flow, a work pistonreciprocably supported in said work cylinder for axial movement therein,means drivingly connected to said work piston, the improvementcomprising, in combination, a piston valve including a control cylinderdisposed parallel to said work cylinder and including a lateral portadjacent to and in alignment with said one lateral port of said workcylinder, :1 control sleeve supported in said control cylinder foradjustment in said control cylinder, said sleeve including a lateralport substantially alignable with said work and control cylinder ports,and a control piston reciprocably supported in said control cylinder andoperatively connected to said means drivingly connected to said workpiston for operation thereby, said control piston including a controledge traversable with respect to said lateral port in said sleeve forcontrolling the fluid flow between said cylinders in timed relation tooperation of said means drivingly connected to said work piston, saidcontrol sleeve lateral port being adjustable for varying the effectiveaxial position of said port in the control sleeve relative to the strokeof said control piston, said control sleeve lateral port having ahelical operative edge, said control piston having a land including acontrol edge of helical form to register with the helical operativeedgeof said port, the control edge of said control piston having anangular extent greater than that of said operative edge of said controlsleeve port, and means for adjusting the angular displacement of saidsleeve about its longitudinal axis.

4. A piston valve according to claim 2 wherein said co-acting fixedformation comprises fixed pin, said valve member including alongitudinal slot in which a terminal end portion of said fixed pin isdisposed for preventing rotation of said valve member about itslongitudinal axis.

References (liter! in the file of this patent UNITED STATES PATENTS1,822,667 Proell Sept. 8, 1931 2,158,342 Trader May 16, 1939 2,322,518Huber June 22, 1943 2,471,117 Orshansky May 24, 1949 2,930,402 GarnetMar. 29, 1960 FOREIGN PATENTS 375,321 France May 24, 1907 635,023 GreatBritain Mar. 29, 1950 780,191 Great Britain July 31, 1957

3. IN A FLUID PRESSURE MACHINE, A CLOSED WORK CYLINDER INCLUDING ATLEAST ONE LATERAL PORT THROUGH WHICH FLUID WILL FLOW, A WORK PISTONRECIPROCABLY SUPPORTED IN SAID WORK CYLINDER FOR AXIAL MOVEMENT THEREIN,MEANS DRIVINGLY CONNECTED TO SAID WORK PISTON, THE IMPROVEMENTCOMPRISING, IN COMBINATION, A PISTON VALVE INCLUDING A CONTROL CYLINDERDISPOSED PARALLEL TO SAID WORK CYLINDER AND INCLUDING A LATERAL PORTADJACENT TO AND IN ALIGNMENT WITH SAID ONE LATERAL PORT OF SAID WORKCYLINDER, A CONTROL SLEEVE SUPPORTED IN SAID CONTROL CYLINDER FORADJUSTMENT IN SAID CONTROL CYLINDER, SAID SLEEVE INCLUDING A LATERALPORT SUBSTANTIALLY ALIGNABLE WITH SAID WORK AND CONTROL CYLINDER PORTS,AND A CONTROL PISTON RECIPROCABLY SUPPORTED IN SAID CONTROL CYLINDER ANDOPERATIVELY CONNECTED TO SAID MEANS DRIVINGLY CONNECTED TO SAID WORKPISTON FOR OPERATION THEREBY, SAID CONTROL PISTON INCLUDING A CONTROLEDGE TRAVERSABLE WITH RESPECT TO SAID LATERAL PORT IN SAID SLEEVE FORCONTROLLING THE FLUID FLOW BETWEEN SAID CYLINDERS IN TIMED RELATION TOOPERATION OF SAID MEANS DRIVINGLY CONNECTED TO SAID WORK PISTON, SAIDCONTROL SLEEVE LATERAL PORT BEING ADJUSTABLE FOR VARYING THE EFFECTIVEAXIAL POSITION OF SAID PORT IN THE CONTROL SLEEVE RELATIVE TO THE STROKEOF SAID CONTROL PISTON, SAID CONTROL SLEEVE LATERAL PORT HAVING AHELICAL OPERATIVE EDGE, SAID CONTROL PISTON HAVING A LAND INCLUDING ACONTROL EDGE OF HELICAL FORM TO REGISTER WITH THE HELICAL OPERATIVE EDGEOF SAID PORT, THE CONTROL EDGE OF SAID CONTROL PISTON HAVING AN ANGULAREXTENT GREATER THAN THAT OF SAID OPERATIVE EDGE OF SAID CONTROL SLEEVEPORT, AND MEANS FOR ADJUSTING THE ANGULAR DISPLACEMENT OF SAID SLEEVEABOUT ITS LONGITUDINAL AXIS.